Cannot apply indexing with [] to an expression of type 'object'

var issNoIP = SplitIssueNoF(txtIssueNo.Text);


issueNoIp stores issueNoIP[0]="value1" and issueNoIP[1]="value2"

now i want to store this value alone issueNoIP[0] into string
like,
string split = Convert.ToString(issNoIP[0]);

if i do so,this is my following error
Error 6 Cannot apply indexing with [] to an expression of type 'object'